1. Field of the Invention
The present invention relates to the field of automatic control on electrical power system, in particular to a bypass type 220V grid voltage sag prevention device and a control method therefor.
2. the Prior Arts
During the normal electrical power supply of a grid, the start-up of reclosers and high-capacity equipment due to short circuit or thunder and lightning weather can cause short-time instability to the voltage of the grid, called “voltage sag”. When system voltage fails to meet the requirement of self perpetuate, an AC contactor controlling a low-voltage electric motor will be released abnormally, thus causing direct damage to continuous production and even threatening personnel safety.
There are several solutions to the release problem of AC contactor caused by voltage sag, including: (1) improve the performance of the contactor; (2) add a control device to the contactor; (3) restart after release. However, these solutions all have shortages. Firstly, the first two improvement solutions will increase the cost of buying components; secondly, there are very few manufacturers having higher production performance or contactors with control devices, thus the selecting range is narrow; thirdly, the control method for restarting after release has impact and will bring damage to the operation of the equipment.